The present invention relates to a switch head for attachment to a temperature sensor with elongated expansion elements having different thermal expansion coefficients and for receiving a device for evaluating the relative movement of the expansion elements.
Cooking areas are frequently made of a glass ceramic plate (Ceran plate) that forms a resting surface for cooking utensils and has a heating space disposed below. Such cooking areas can be heated in different ways, for example with an electric resistive heating element, halogen lamps, gas and the like. Regardless of the heating mode, the Ceran plate can be damaged or destroyed by excess heat, so that overheating has to be avoided.
For this purpose, temperature limiters are frequently used, which comprise a temperature sensor and a switch head of the type described above, which is connected with the temperature sensor. The temperature sensor is arranged in the heating space underneath the Ceran plate and is therefore exposed to substantially the same temperature as the Ceran plate.
When the temperature sensor heats up, the sensor component which can move relative to the switch head is displaced relative to the switch head, and the relative movement is transmitted to a switch via a mechanical connectionxe2x80x94which can be a simple ram. When the temperature sensor senses that the temperature of the Ceran plate may become too high, the aforedescribed relative movement becomes so large that the switch is actuated, which decreases or disconnects the heating power supplied to the heating element.
When the cooking area is heated electrically, power can be disconnected simply by forming the switch as a normally closed switch connected in series with the heater. When the cooking area is heated with gas, then actuation of the switch closes a valve arranged in the gas supply line.
AT 404 776 describes combined switch heads which satisfy the aforedescribed function to prevent overheating. These switch heads also provide a so-called xe2x80x9cheat indicatorxe2x80x9d which warns the user not to touch a section of the cooking area that is too hot. In addition, switch heads for temperature limiters are known which combine different additional functions.
All these embodiments, however, have in common that the switch head is formed as a single piece, which makes it impossible to enhance a switch head by adding additional functions. As a result, dedicated production lines and inventory have to be provided for each combination of those functions.
It would therefore be desirable and advantageous to provide an improved switch head which obviates the prior art shortcomings and allows easy implementation of additional functions. It would also be desirable to provide a modular temperature controller in which additional functions can be incorporated.
The invention is directed to a switch head and a temperature controller/limiter with such switch head, wherein additional functions can be the added or removed.
According to an aspect of the invention, attachment means are provided for attaching at least one additional switch head to an existing switch head. Moreover, at least one opening is provided adapted to receive a transfer member for transferring the relative movement of the expansion elements to the at least one additional switch head. In this way, the switch head can be used as an additional module for a temperature limiter.
According to one embodiment of the invention, the opening can be formed by eliminating a sidewall of the switch head, allowing a lightweight construction of the component.
According to another embodiment of the invention, an electric switching contact can be installed in the switch head for evaluating the relative movement. This arrangement provides a very simple temperature limiter, for example by connecting the switching contact in series with the resistive heating element for the cooking area.
According to yet another embodiment of the invention, the relative displacement of the expansion elements can be transferred to a device for evaluating the relative displacement. A transfer member in the form of a ram can be implemented which is moveable along with longitudinal axis in the switch head. This allows advantageously a particularly rigid and simple construction and makes it unnecessary to install an additional transfer member when the additional switch head is attached to a first switch head.
According to another embodiment of the invention, the switch heads can be covered by a cover that can be easily removed. This cover protects the first switch head from contamination and debris if no other switch head is attached to the first switch head.
According to another aspect of the invention, a temperature limiter includes a temperature sensor with elongated expansion elements having different thermal expansion coefficients and a switch head arranged in a second end region of the temperature sensor, wherein the switch head includes a device that evaluates the relative displacement of the expansion elements.
As mentioned above, such temperature limiters are known for overtemperature protection of glass ceramic cooking areas. A combination of a temperature limiter with a heat indicator is also known. However, these conventional devices do not allow a modular extension or any change in the functionality of the switch heads, such as adding or subtracting functions.
The temperature limiter of the invention includes an additional switch head with an additional device for measuring the relative displacement of the expansion elements, which the additional switch head connected to the first switch head.
In this way, the temperature limiter can be easily modified by removing the second switch head. Alternatively, additional modules can be attached to the temperature limiter.
According to another embodiment of the invention, an additional module can be provided which includes a basic module preferably made of ceramic and provided with a bore, wherein the additional module is placed over the temperature sensor by means of the bore. This provides additional functions in the region of the temperature sensor.
According to another embodiment of the invention, the additional module can be connected directly with the switch head. This provides a particularly rigid connection between the additional module and the temperature limiter.
According to another embodiment of the invention, a resistor, preferably an ohmic resistor with a temperature-dependent resistance value, can be attached to the basic module of the additional module. This enables very precise temperature measurements.
According to another embodiment of the invention, the resistor can be formed by a resistive paste which is printed onto the basic module, preferably by screen printing, which advantageously makes the design very compact. Moreover, the resistor in this embodiment can be manufactured in a single manufacturing step and attached on the basic module, thereby obviating the need for a separate process for attaching the resistor. A suitable range for the resistance value and its temperature dependence can be defined by selecting a suitable material and resistive path of the paste.
According to another embodiment of the invention, the resistor can be shielded by a heat shield to prevent the resistor from heating too quickly during the heat up process.
According to yet another embodiment of the invention, the additional module can include two electrodes attached to the basic module and forming an arc gap therebetween. This makes it possible to provide in the gas-heated cooking areas not only a aforedescribed temperature limiter, but also a device for igniting the gas inside the heating space.
According to another embodiment of the invention, the additional module can include a resistive heating element which can be attached to the basic module and implemented preferably as a helical coil. This type of heating element has a particularly simple construction and is therefore more reliable and more easily controlled as compared to other arrangements, such as a spark plug.